Toggle Combobox!
<br>
<button cdkCombobox #trigger="cdkCombobox" class="example-combobox" [cdkComboboxTriggerFor]="panel" [openActions]="'toggle'">
    No Value
</button>

<ng-template #panel>
    <div cdkComboboxPopup [firstFocus]="input">
        <input #input>
        <button (click)="trigger.updateAndClose(input.value)">Apply</button>
    </div>
</ng-template>
